I haven't tried to redeem to Europe for a couple of years, but needed a one way in late June to link up to a superb ex-CDG RT in J on AF. I was stunned that I was able to find an AA J award PHL-MAN on the exact day I wanted and could make it PHL-MAN-LHR-STR. (I had been planning on driving a rental car to IAD and flying VS PE IAD-LHR on award, with YQ.) I will have to position RDU-PHL the night before but I haven't been in Philly for a few years and will enjoy the vacation day.
I have always found that booking 5 months out was the sweet spot for me between flexibility, availability, and ability to commit to specific dates.